Unlike passive transponders which draw their energy from received electromagnetic signals, an active transponder has an internal electric power supply which powers the electronic circuits independently of the level of induced voltage in the antenna of the transponder.
The active transponder may take different forms, in particular the form of a card, electronic tag, and more generally a portable unit. The transponder can operate in modes requiring different degrees of security, in particular for the different applications for which the transponder is intended. Controlling the security of an application may exist at different levels, in particular the communication protocol. In the case of the present invention, one is concerned in particular with controlling the security of an operating mode or a selected application by limiting the communication distance between a reader which transmits with a given power and the transponder.
The present invention thus proposes answering the security problem generated by a multi-application active transponder. It is proposed, in particular, to integrate in the same transponder applications of the “access to a building or means of transport” type and of the banking type for monetary transactions requiring a high level of security. For obvious reasons, it is clear that the maximum communication distance between a transponder and a transceiver, hereinafter a “reader”, constitutes an important parameter.
A particular object of the present invention is to provide an active transponder intended for various applications requiring different degrees of security and the arrangement of which is relatively easy and inexpensive, while assuring a high level of efficiency for controlling the various degrees of security required.